Telecommunication systems are used to transmit information between communication devices. In order to handle transmission demands, telecommunication systems have become increasingly complex. Presently, telecommunication systems employ processor driven devices which exchange information by transferring the information using overlapping frequencies carried on a single transmission line. In systems using overlapping frequencies to exchange information, some of the frequencies are reserved for signaling (i.e., signaling frequencies). Through the use of indicators at the signaling frequencies, processors within the telecommunication systems set up, control, and terminate the exchange of information over the transmission line.
In a typical telecommunication system employing signaling, a processor at telephone company central office (TCCO) will generate tones (i.e., indicators) for detection by a processor at a user site. The signaling tones take the form of increased voltage levels at corresponding signaling frequencies, with the processor at the user site monitoring the signaling frequencies for the increased voltage levels. In addition to setting up, controlling, and terminating the exchange of information, new standards are being developed (such as standard G.994.1-Handshake Procedures for Digital Subscriber Line (DSL) Transceivers developed by the International Telecommunications Union (ITU), incorporated fully herein by reference) which require the processor to wake up in response to receiving signaling tones.
These new standards are problematic for modem computer systems which switch to a low power state (e.g., “sleep mode”) during periods when the full processing power of the processor is not required in order to conserve energy. In present computer systems, when the DSP is in a sleep mode, the DSP is unable to perform signal detection. Therefore, in order to comply with developing standards while allowing computer systems to take advantage of placing processors in a sleep mode, an alternative method and apparatus for signal detection is required.
FIG. 1 depicts an example of a list of signaling frequencies 30 from standard G.994.1 which can be used for signaling in a telecommunication system. Each signaling frequency in the list 30 corresponds to a signaling bin from a signaling bin list 20. For example, a signaling frequency of 172.5 kHz corresponds to signaling bin number 40. Between each signaling bin depicted in signaling bin list 20 are one or more bins (not shown) which are used for transmitting data. For example, the next bin illustrated after bin number 40 from signaling bin list 20 is bin number 56; thus, from this drawing it can be seen that bins 41-55 are not used for signaling. Typically, each bin is separated from an adjacent bin by a specified distance (e.g., 4.3125 kHz in standard G.994.1). Accordingly, if the bins are 4.3125 kHz apart, bin number 41 is located at 176.8125 kHz (172.5+4.3125).
Prior to transmitting data, the telecommunication system will enter a set-up period in which information is exchanged between the processor residing at the user site and the processor at the TCCO. The set-up period provides for “handshaking” between the processors in order to optimize the connection between them for carrying data. During the setup period, the data transmission bins which are not used for signaling will reflect only noise on the transmission line and, therefore, can be used as a reference for detecting whether a signaling tone, identified by an increased voltage level, is present on an adjacent signaling bin from the signaling list 20.
In accordance with standard G.994.1, the signaling bins in signaling bin list 20 may be used to designate the presence of incoming data through the presence or absence of an indicator on a corresponding signaling frequency. For example, an indicator at 172.5 kHz in bin number 40 may indicate that additional data will soon follow, whereas the absence of an indicator in bin number 40 will indicate that additional data is not currently on its way. This information (presence or absence of an indicator) can be used by the processor to reallocate resources to interpret data received from the TCCO. In addition, standard G.994.1 allocates one or more bins for “waking up” a processor which is in a sleep mode. Unfortunately, present processors are unable to detect signaling tones while in a sleep mode and, hence, would be unable to wake up if an appropriate indicator were sent.
FIG. 2 depicts a prior art system for interpreting the signaling frequencies such as those depicted in signaling frequency list 30 (FIG. 1) carried by a signal on a transmission line 38. In a system such as the one depicted in FIG. 2, the incoming signal is first passed through a low pass filter (LPF) 40 to remove high frequencies contained within the incoming signal on the transmission line 38 that can be attributed to noise and which may result in aliasing (i.e., relatively high frequencies being confused by system circuits as lower frequency signals). The filtered signal is then passed through an analog-to digital (A/D) converter 50 to convert the filtered signal from an analog domain to a digital domain, thereby creating a filtered digital signal at a connection 58 for processing by a digital signal processor (DSP) 60.
The DSP 60 processes the filtered digital signal at the DSP connection 58 to detect and interpret signaling tones present on one or more of the plurality of signaling frequencies. In the systems depicted in FIG. 2, the A\D converter 50 operates at a relatively high sampling frequency (typically many times higher than the highest signaling frequency) to generate a filtered digital signal at the DSP connection 58 having a suitable signal-to-noise ratio (SNR) for data processing by the DSP 60.
Using the DSP 60 to determine if signaling tones are present on one or more of the plurality of signaling frequencies 30, however, requires system power and processing power. The DSP 60 consumes system power and uses processing power to continuously monitor the filtered digital signal for signaling frequencies 30. Therefore, the DSP 60 cannot be allowed to enter a sleep mode during periods when a signaling indicator may be received. In addition, since the power consumption of an A\D converter is approximately proportional to its sampling rate, the A\D converter 50 consumes a relatively high amount of power due to the relatively high sampling rate at which it operates to supply a filtered digital signal with a suitable SNR for the DSP 60.
Many present day computer systems allow the DSP 60 to switch to sleep mode when the DSP 60 is not in use. In sleep mode, the DSP 60 performs only the most essential tasks and, therefore, draws a minimal amount of power. This mode is desirable for conserving energy and battery life. As noted above, however, in sleep mode the DSP 60 is unable to monitor the filtered digital signal at the DSP connection 58 for signaling tones, thereby missing signaling tones. Since the DSP 60 is unable to detect signaling tones in sleep mode, the DSP 60 will not be allowed to enter “sleep mode” when used with new standards such as G994.1 mentioned above.
It is desirable to allow digital signal processors DSP's to enter a low power consumption state while still being able to detect the presence of signaling tones in order to conserve power and to conform to developing standards. Accordingly, there is a need for a low power detection method and apparatus for detecting signaling tones without the use of a system's DSP. The present invention fulfils this need, among others.